The present patent application relates to a seal assembly for installation on shafts of mixers for concrete, mortar and similar mixtures, in order to prevent the mixture from reaching the shaft bearing.
Mixers comprise large tanks provided with rotating arms for the continuous mixing of concrete until the desired mixture is obtained. In each mixer, the arms are actuated by a shaft with horizontal axis arranged across the tank by means of suitable attachment holes located on two opposite walls of the tank.
The two ends of the shaft are supported by support assemblies with bearing, located just outside the external edge of the tank. Seal assemblies are installed on the attachment holes located on two opposite tank walls to prevent the fluid or dry mass from leaking out of the tank through the small space that exists between the shaft and its attachment holes.
In fact, in such a case the mixture leakage would inevitably flow towards the outside along the rotating shaft, reaching the bearing contained in the adjacent support assembly.
Obviously, this could cause great damage since, after penetrating into the bearing, the concrete would create friction, impair rotation and cause breakage. In order to prevent this from occurring, the traditional technology provides for the installation of a seal assembly on each attachment holes of the shaft on mixer tanks.
The known types of seal assemblies operate according to the so-called sliding seal principle. They comprise two rings with front sliding surfaces in oil bath. One of the rings is rigidly fixed to the body of the seal block and the other ring is joined to the shaft and therefore rotates with the shaft around the same axis.
As it is known, the two sliding rings are capable of ensuring seal for two different reasons. First of all, they are tightly pressed one against the other. Furthermore, their contact surfaces feature a very fine finish (technically defined as lapping) that allows for completely eliminating surface irregularities that could impair the perfect adhesion of the opposite sides of the two rings, thus creating a loss of seal in those points.
Moreover, according to the current technology, seal assemblies are one-piece constructions that comprise the block with bearing that supports one end of the shaft.
The purpose of the present invention is to modify the traditional technology in order to prevent any risk of concrete leakage from the mixing tank towards the shaft support bearing.
Based on the results of an accurate study, leakage is sometimes due to a seal failure of the two sliding rings. Most of the times, the imperfect seal of the two rings is due to the incorrect coupling between the sealing assembly and the rotating shaft during the assembling operations of the mixer which are mainly carried out manually.
Since the seal assembly also incorporates the block with the bearing, it is easy to understand how large and heavy this one-piece component is, also in view of the very large dimensions of concrete mixers.
The great difficulties in the manipulation of such a large, heavy component does not allow for the perfect coupling between the seal assembly and its shaft, impairing the concentricity of the two seal rings.
The slightest inaccuracy during the coupling operation may result in a loss of seal between the two lapped surfaces of the sliding rings when mixing. This may cause dangerous concrete leakage on the outside of the tank towards the bearing.
According to the present invention, two different solutions are possible. In the first solution, the seal assembly includes another gasket with optimal sealing capacities. In the second solution, the seal assembly is separated from the assembly that houses the bearing, in order to provide two different components with reduced dimensions and weight, for easier manipulation during the manual assembling operations.
In particular, the additional gasket according to the present invention is located in internal position with respect to the mixing tank, compared to the position of the traditional sliding seals. Moreover, the additional gasket is assisted by a grease/oil forced lubrication system that, as explained later on in the text, acts as an additional barrier against concrete leakage from the inside to the outside of the tank.
On the other hand, the reduced weight and increased manoeuvrability of the seal assembly according to the present invention (being separated from the bearing support assembly) allows the operators to perfectly couple the seal assembly with the rotating shaft, thus ensuring optimal installation and total seal.